Gclc

Summary

Gene Symbol: Gclc
Description: glutamate-cysteine ligase, catalytic subunit
Alias: Glclc, glutamate--cysteine ligase catalytic subunit, GCS heavy chain, Glutamylcysteine gamma synthetase light chain, gamma-ECS, gamma-glutamylcysteine synthetase
Species: rat
Products:     Gclc

Top Publications

  1. McKone E, Shao J, Frangolias D, Keener C, Shephard C, Farin F, et al. Variants in the glutamate-cysteine-ligase gene are associated with cystic fibrosis lung disease. Am J Respir Crit Care Med. 2006;174:415-9 pubmed
    ..between CF lung disease and a functional polymorphism in the glutamate-cysteine ligase catalytic subunit (GCLC) gene...
  2. Koide S, Kugiyama K, Sugiyama S, Nakamura S, Fukushima H, Honda O, et al. Association of polymorphism in glutamate-cysteine ligase catalytic subunit gene with coronary vasomotor dysfunction and myocardial infarction. J Am Coll Cardiol. 2003;41:539-45 pubmed
    ..test the hypothesis that polymorphisms in the promoter region of the glutamate-cysteine ligase catalytic subunit (GCLC) gene may be associated with coronary endothelial vasomotor dysfunction and myocardial infarction (MI)...
  3. Yan N, Meister A. Amino acid sequence of rat kidney gamma-glutamylcysteine synthetase. J Biol Chem. 1990;265:1588-93 pubmed
    ..This amino acid sequence shows extremely low overall similarity to that of gamma-glutamylcysteine synthetase isolated from Escherichia coli. ..
  4. Konsavage W, Zhang L, Wu Y, Shenberger J. Hyperoxia-induced activation of the integrated stress response in the newborn rat lung. Am J Physiol Lung Cell Mol Physiol. 2012;302:L27-35 pubmed publisher
    ..These findings demonstrate that Ox activates the ISR within the newborn lung and highlight regional and cell-specific alterations in the expression ISR transcription factors that regulate redox balance. ..
  5. Dasgupta A, Das S, Sarkar P. Thyroid hormone promotes glutathione synthesis in astrocytes by up regulation of glutamate cysteine ligase through differential stimulation of its catalytic and modulator subunit mRNAs. Free Radic Biol Med. 2007;42:617-26 pubmed
    ..Quantitative RT-PCR analysis revealed that astrocytes contained a basal excess of GCLC (catalytic subunit of GCL) mRNA, relative to GCLM (modulator subunit of GCL) mRNA, the ratio being 4:1...
  6. Ray S, Watkins D, Misso N, Thompson P. Oxidant stress induces gamma-glutamylcysteine synthetase and glutathione synthesis in human bronchial epithelial NCI-H292 cells. Clin Exp Allergy. 2002;32:571-7 pubmed
    ..Bronchial epithelial (NCI-H292) cells respond rapidly and sensitively to oxidant stress, and this adaptive response is mediated by increased gamma-GCS mRNA transcription and enzyme activity. ..
  7. Thompson S, White C, Krejsa C, Eaton D, Kavanagh T. Modulation of glutathione and glutamate-L-cysteine ligase by methylmercury during mouse development. Toxicol Sci. 2000;57:141-6 pubmed
    ..Western and Northern blots for Glcl-catalytic (Glclc) and Glcl-regulatory (Glclr) subunits were performed on gd 12 and gd 16 fetuses...
  8. Gualtieri A, Mazzone G, Rey R, Schteingart H. FSH and bFGF stimulate the production of glutathione in cultured rat Sertoli cells. Int J Androl. 2009;32:218-25 pubmed
    ..Intracellular GSH content is maintained by de novo synthesis, involving glutamate-cysteine ligase catalytic (GCLC) and modulatory (GCLM) subunits, and by recycling from oxidized GSH, catalysed by glutathione reductase (GR)...
  9. Lee J, Kang J, Stipanuk M. Differential regulation of glutamate-cysteine ligase subunit expression and increased holoenzyme formation in response to cysteine deprivation. Biochem J. 2006;393:181-90 pubmed
    GCL (glutamate-cysteine ligase) is a heterodimer of a GCLC (GCL catalytic subunit) that possesses all of the enzymatic activity and a GCLM (GCL modifier subunit) that alters the K(i) of GCLC for GSH...

More Information

Publications58

  1. Manna S, Kuo M, Aggarwal B. Overexpression of gamma-glutamylcysteine synthetase suppresses tumor necrosis factor-induced apoptosis and activation of nuclear transcription factor-kappa B and activator protein-1. Oncogene. 1999;18:4371-82 pubmed
    ..Overall, our results indicate that most of the pleiotropic actions of TNF are regulated by the glutathione-controlled redox status of the cell. ..
  2. Zhang S, Li H, Zhang L, Li J, Wang R, Wang M. Effects of troxerutin on cognitive deficits and glutamate cysteine ligase subunits in the hippocampus of streptozotocin-induced type 1 diabetes mellitus rats. Brain Res. 2017;1657:355-360 pubmed publisher
    ..aimed to determine the effects of troxerutin on cognitive deficits and glutamate cysteine ligase subunits (GCLM and GCLC) in the hippocampus of streptozotocin-induced type 1 diabetes mellitus (T1DM) rats...
  3. Zhao Y, Chen L, Gao S, Toselli P, Stone P, Li W. The critical role of the cellular thiol homeostasis in cadmium perturbation of the lung extracellular matrix. Toxicology. 2010;267:60-9 pubmed publisher
    ..Thus, Cd upregulation of cellular thiols may be a critical cellular event facilitating downregulation of LO, a potential mechanism for Cd-induced emphysema. ..
  4. Diaz Hernandez J, Almeida A, Delgado Esteban M, Fernandez E, Bolanos J. Knockdown of glutamate-cysteine ligase by small hairpin RNA reveals that both catalytic and modulatory subunits are essential for the survival of primary neurons. J Biol Chem. 2005;280:38992-9001 pubmed
    ..Thus, specific and independent disruption of each subunit of GCL in neurons can be said to cause a primary decrease in glutathione that is sufficient to promote neurodegeneration. ..
  5. Li S, Li X, Rozanski G. Regulation of glutathione in cardiac myocytes. J Mol Cell Cardiol. 2003;35:1145-52 pubmed
    ..These signaling mechanisms may play essential roles in controlling intracellular redox state and normal function of cardiac myocytes. ..
  6. Ramani K, Tomasi M, Yang H, Ko K, Lu S. Mechanism and significance of changes in glutamate-cysteine ligase expression during hepatic fibrogenesis. J Biol Chem. 2012;287:36341-55 pubmed publisher
    ..Expression of the GCL catalytic subunit (GCLC) fell during HSC activation and increased when activated HSCs revert back to quiescence...
  7. Beutler E, Moroose R, Kramer L, Gelbart T, Forman L. Gamma-glutamylcysteine synthetase deficiency and hemolytic anemia. Blood. 1990;75:271-3 pubmed
    ..This leads us to conclude that either the occurrence of neurologic symptoms in the other reported family was a chance association or that the clinical expression of this rare defect is pleomorphic. ..
  8. Cheng L, Li B, Luo J, Tu H, Liu Q, Ran P. Identification of an E-box motif as a transcriptional repressor element in the proximal promoter region of the GCLC gene in rat lung epithelial L2 cells. Free Radic Biol Med. 2005;39:1030-40 pubmed
    ..GCL is made up of two differentially regulated subunits, a catalytic or heavy subunit (GCLC) and a modifier or light subunit (GCLM)...
  9. Shi Z, Osei Frimpong J, Kala G, Kala S, Barrios R, Habib G, et al. Glutathione synthesis is essential for mouse development but not for cell growth in culture. Proc Natl Acad Sci U S A. 2000;97:5101-6 pubmed
    ..These data demonstrate that GSH is required for mammalian development but dispensable in cell culture and that the functions of GSH, not GSH itself, are essential for cell growth. ..
  10. Shukla G, Chiu J, Hart B. Enhanced expression of pulmonary gamma-glutamylcysteine synthetase heavy subunit in rats exposed to cadmium aerosols. Toxicol Appl Pharmacol. 2000;163:249-59 pubmed
    ..These observations suggest that resistance to Cd toxicity in the lung may reflect the ability of specific lung cells to upregulate gamma-GCS expression and increase de novo GSH synthesis as an adaptive response. ..
  11. Li M, Jang J, Na H, Cha Y, Surh Y. Carbon monoxide produced by heme oxygenase-1 in response to nitrosative stress induces expression of glutamate-cysteine ligase in PC12 cells via activation of phosphatidylinositol 3-kinase and Nrf2 signaling. J Biol Chem. 2007;282:28577-86 pubmed
    ..This was accompanied by increased expression of the catalytic subunit of glutamate-cysteine ligase (GCLC), the rate-limiting enzyme in GSH biosynthesis...
  12. Habib G, Shi Z, Lieberman M. Glutathione protects cells against arsenite-induced toxicity. Free Radic Biol Med. 2007;42:191-201 pubmed
    ..Further, protection from arsenite-induced ubiquitination is mediated by GSH and to a lesser extent by available reducing equivalents in the cells. ..
  13. Xiong L, Yu L, Li B, Ran P. [Effect of allitridum on expression of the gamma-glutamyl-cysteine synthetase in rat lung epithelial L2 cells]. Zhonghua Jie He He Hu Xi Za Zhi. 2006;29:368-71 pubmed
    ..82 - 9.92, P < 0.05). Allitidum may increase the antioxidative ability of CCL-149 cells by increasing the expression of gamma-GCS protein and the content of GSH. ..
  14. Chen Y, Shertzer H, Schneider S, Nebert D, Dalton T. Glutamate cysteine ligase catalysis: dependence on ATP and modifier subunit for regulation of tissue glutathione levels. J Biol Chem. 2005;280:33766-74 pubmed
    ..gamma-GC may be produced by the catalytic subunit GCLC or by the holoenzyme (GCLholo), which comprises GCLC and the modifier subunit GCLM...
  15. Hui L, Hong Y, Jingjing Z, Yuan H, Qi C, Nong Z. HGF suppresses high glucose-mediated oxidative stress in mesangial cells by activation of PKG and inhibition of PKA. Free Radic Biol Med. 2010;49:467-73 pubmed publisher
    ..Moreover, Rp-8-pCPT-cGMPS blocked HGF-increased glutamate-cysteine ligase catalytic subunit (GCLC) expression in HG-treated RMC through enhancement of USF binding to the negative regulatory region of the GCLC ..
  16. Dalton T, Dieter M, Yang Y, Shertzer H, Nebert D. Knockout of the mouse glutamate cysteine ligase catalytic subunit (Gclc) gene: embryonic lethal when homozygous, and proposed model for moderate glutathione deficiency when heterozygous. Biochem Biophys Res Commun. 2000;279:324-9 pubmed
    ..GCL is the rate-limiting step and represents a heterodimeric enzyme comprised of a catalytic subunit (GCLC) and a ("regulatory"), or modifier, subunit (GCLM)...
  17. Marson F, Bertuzzo C, Ribeiro A, Ribeiro J. Polymorphisms in the glutathione pathway modulate cystic fibrosis severity: a cross-sectional study. BMC Med Genet. 2014;15:27 pubmed publisher
    ..We analyzed CFTR mutations, polymorphisms (GSTM1 and GSTT1 deletions, GSTP1 + 313A > G, GCLC-129C > T, and GCLC-3506A > G) in modifier genes and CF clinical severity as assessed by 28 clinical and ..
  18. Guerrero Beltrán C, Calderon Oliver M, Martínez Abundis E, Tapia E, Zarco Márquez G, Zazueta C, et al. Protective effect of sulforaphane against cisplatin-induced mitochondrial alterations and impairment in the activity of NAD(P)H: quinone oxidoreductase 1 and ? glutamyl cysteine ligase: studies in mitochondria isolated from rat kidney and in LLC-PK1 . Toxicol Lett. 2010;199:80-92 pubmed publisher
    ..It is concluded that the protection exerted by SFN on mitochondrial alterations and NQO1 and ?GCL enzymes may be involved in the renoprotection of SFN against CIS. ..
  19. Shenvi S, Smith E, Hagen T. Transcriptional regulation of rat gamma-glutamate cysteine ligase catalytic subunit gene is mediated through a distal antioxidant response element. Pharmacol Res. 2009;60:229-36 pubmed publisher
    ..detoxification gene, the transcriptional regulation of the rat gamma-glutamate cysteine ligase catalytic subunit (GCLC) is controversial...
  20. Galloway D, Blake D, McLellan L. Regulation of gamma-glutamylcysteine synthetase regulatory subunit (GLCLR) gene expression: identification of the major transcriptional start site in HT29 cells. Biochim Biophys Acta. 1999;1446:47-56 pubmed
    ..The transcriptional activity of the GLCLR gene was increased by approximately 2.5-fold in SNP-treated cells. ..
  21. Yang Y, Dieter M, Chen Y, Shertzer H, Nebert D, Dalton T. Initial characterization of the glutamate-cysteine ligase modifier subunit Gclm(-/-) knockout mouse. Novel model system for a severely compromised oxidative stress response. J Biol Chem. 2002;277:49446-52 pubmed
    ..In higher eukaryotes, this enzyme is a heterodimer comprising a catalytic subunit (GCLC) and a modifier subunit (GCLM), which change the catalytic characteristics of the holoenzyme...
  22. Kuo M, Bao J, Curley S, Ikeguchi M, Johnston D, Ishikawa T. Frequent coordinated overexpression of the MRP/GS-X pump and gamma-glutamylcysteine synthetase genes in human colorectal cancers. Cancer Res. 1996;56:3642-4 pubmed
    ..78 for all of the tumor samples studied. These results strongly suggest that MRP and gamma-GCS genes are coordinately up-regulated during colorectal carcinogenesis...
  23. Beutler E, Gelbart T, Kondo T, Matsunaga A. The molecular basis of a case of gamma-glutamylcysteine synthetase deficiency. Blood. 1999;94:2890-4 pubmed
    ..The partial genomic structure of the catalytic subunit of gamma-glutamylcysteine synthetase (GLCLC) was determined, providing some intron/exon boundaries to make it possible to sequence an affected part of the ..
  24. Kim S, Woodcroft K, Khodadadeh S, Novak R. Insulin signaling regulates gamma-glutamylcysteine ligase catalytic subunit expression in primary cultured rat hepatocytes. J Pharmacol Exp Ther. 2004;311:99-108 pubmed
    ..observed in diabetic patients, and insulin reportedly increases GSH synthesis via increased GCL catalytic subunit (GCLC) gene expression...
  25. Akai S, Hosomi H, Minami K, Tsuneyama K, Katoh M, Nakajima M, et al. Knock down of gamma-glutamylcysteine synthetase in rat causes acetaminophen-induced hepatotoxicity. J Biol Chem. 2007;282:23996-4003 pubmed
    ..An adenovirus vector with short hairpin RNA against rat gamma-GCS heavy chain subunit (GCSh) (AdGCSh-shRNA) was constructed and used to knock down the GCSh...
  26. Hamilton D, Wu J, Alaoui Jamali M, Batist G. A novel missense mutation in the gamma-glutamylcysteine synthetase catalytic subunit gene causes both decreased enzymatic activity and glutathione production. Blood. 2003;102:725-30 pubmed
  27. Li J, Dai A, Hu R, Zhu L, Tan S. Positive correlation between PPARgamma/PGC-1alpha and gamma-GCS in lungs of rats and patients with chronic obstructive pulmonary disease. Acta Biochim Biophys Sin (Shanghai). 2010;42:603-14 pubmed publisher
    ..The activation of the PPARgamma/PGC-1alpha pathway may protect against COPD progression by upregulating gamma-GCS and relieving oxidative stress. ..
  28. Lickteig A, Fisher C, Augustine L, Cherrington N. Genes of the antioxidant response undergo upregulation in a rodent model of nonalcoholic steatohepatitis. J Biochem Mol Toxicol. 2007;21:216-20 pubmed
    ..the antioxidant response, including NAD(P)H:quinone oxidoreductase-1 (Nqo1), Glutamate cysteine ligase catalytic (Gclc), and Heme oxygenase-1 (Ho-1), were significantly induced in MCD rat liver but not in HF rat liver...
  29. Botta D, Franklin C, White C, Krejsa C, Dabrowski M, Pierce R, et al. Glutamate-cysteine ligase attenuates TNF-induced mitochondrial injury and apoptosis. Free Radic Biol Med. 2004;37:632-42 pubmed
    ..The rate-limiting enzyme in GSH synthesis is glutamate-cysteine ligase (GCL), which is composed of catalytic (GCLC) and modifier (GCLM) subunits...
  30. Hu G, Zhou Y, Hong W, Tian J, Hu J, Peng G, et al. Development and systematic oxidative stress of a rat model of chronic bronchitis and emphysema induced by biomass smoke. Exp Lung Res. 2013;39:229-40 pubmed publisher
    ..The glutamate-cysteine ligase catalytic subunit (GCLC) protein expression in the lung was measured using immunohistochemistry and western blotting...
  31. Jang H, Do G, Lee H, Ok H, Shin J, Kwon O. Schisandra Chinensis Baillon regulates the gene expression of phase II antioxidant/detoxifying enzymes in hepatic damage induced rats. Nutr Res Pract. 2014;8:272-7 pubmed publisher
    ..enzyme expression, such as glutathione S-transferase (GST) and glutamate-cysteine ligase catalytic subunit (GCLC)...
  32. Yang H, Zeng Y, Lee T, Yang Y, Ou X, Chen L, et al. Role of AP-1 in the coordinate induction of rat glutamate-cysteine ligase and glutathione synthetase by tert-butylhydroquinone. J Biol Chem. 2002;277:35232-9 pubmed
    ..In conclusion, AP-1 is required for basal expression of GCL and GS; while NF1 serves as a repressor of GS, increased AP-1 transactivation is the predominant mechanism for coordinate induction of GCL and GS expression by TBH. ..
  33. Tsai Turton M, Luderer U. Gonadotropin regulation of glutamate cysteine ligase catalytic and modifier subunit expression in rat ovary is subunit and follicle stage specific. Am J Physiol Endocrinol Metab. 2005;289:E391-402 pubmed
    ..GSH) and protein levels of the catalytic and modifier subunits of the rate-limiting enzyme in GSH synthesis, GCLc and GCLm, increase in immature rat ovaries after treatment with gonadotropin...
  34. Tsuchiya K, Mulcahy R, Reid L, Disteche C, Kavanagh T. Mapping of the glutamate-cysteine ligase catalytic subunit gene (GLCLC) to human chromosome 6p12 and mouse chromosome 9D-E and of the regulatory subunit gene (GLCLR) to human chromosome 1p21-p22 and mouse chromosome 3H1-3. Genomics. 1995;30:630-2 pubmed
  35. Li M, Chiu J, Kelsen A, Lu S, Fukagawa N. Identification and characterization of an Nrf2-mediated ARE upstream of the rat glutamate cysteine ligase catalytic subunit gene (GCLC). J Cell Biochem. 2009;107:944-54 pubmed publisher
    ..on genes for most phase II detoxification enzymes, including the glutamate cysteine ligase catalytic subunit (GCLC)...
  36. Chen C, Brown Borg H, Rakoczy S, Ferrington D, Thompson L. Aging impairs the expression of the catalytic subunit of glutamate cysteine ligase in soleus muscle under stress. J Gerontol A Biol Sci Med Sci. 2010;65:129-37 pubmed publisher
    ..The protein content of the two subunits of GCL, catalytic subunit (GCLC) and modifier subunit (GCLM), were evaluated...
  37. Mishra M, Zhong Q, Kowluru R. Epigenetic modifications of Nrf2-mediated glutamate-cysteine ligase: implications for the development of diabetic retinopathy and the metabolic memory phenomenon associated with its continued progression. Free Radic Biol Med. 2014;75:129-39 pubmed publisher
    ..The transcriptional factor Nrf2 regulates the expression of Gclc, the enzyme important in the biosynthesis of GSH, and in diabetes the binding of Nrf2 at the antioxidant response ..
  38. Luderer U, Diaz D, Faustman E, Kavanagh T. Localization of glutamate cysteine ligase subunit mRNA within the rat ovary and relationship to follicular apoptosis. Mol Reprod Dev. 2003;65:254-61 pubmed
    ..was used to localize ovarian mRNA expression of the catalytic and modulatory subunits of glutamate cysteine ligase (Gclc and Gclm), the rate-limiting enzyme in GSH synthesis, during each stage of the rat estrous cycle...
  39. Ristoff E, Augustson C, Geissler J, de Rijk T, Carlsson K, Luo J, et al. A missense mutation in the heavy subunit of gamma-glutamylcysteine synthetase gene causes hemolytic anemia. Blood. 2000;95:2193-6 pubmed
    ..Several family members with half-normal GCS activity in their erythrocytes were heterozygous for the mutation. ..
  40. Yerrapureddy A, Tobias J, Margulies S. Cyclic stretch magnitude and duration affect rat alveolar epithelial gene expression. Cell Physiol Biochem. 2010;25:113-22 pubmed publisher
  41. Fernandes C, Rong L, Tamura T, Stewart K, Rogers L, McMicken H, et al. Stable transfection of Chinese hamster ovary cells with glutamate-cysteine ligase catalytic subunit cDNA confers increased resistance to tert-butyl hydroperoxide toxicity. Toxicol Lett. 2002;136:107-20 pubmed
    ..we used liposome-mediated transfer of the cDNA for rat glutamate-cysteine ligase (GLCL) catalytic subunit (GLCLC) to transfect Chinese hamster ovary (CHO) cells. CHO cell lines (CHOhi) with stably enhanced GLCL activities (14...
  42. Yang L, Chen J, Xu T, Zhou A, Yang H. Rice protein improves oxidative stress by regulating glutathione metabolism and attenuating oxidative damage to lipids and proteins in rats. Life Sci. 2012;91:389-394 pubmed publisher
    ..In the liver, the total antioxidative capacity (T-AOC), mRNA levels of glutamate cysteine ligase catalytic subunit (GCLC) and glutamate cysteine ligase modulatory subunit (GCLM), and the activities of hepatic catalase (CAT), total ..
  43. Yang H, Magilnick N, Lee C, Kalmaz D, Ou X, Chan J, et al. Nrf1 and Nrf2 regulate rat glutamate-cysteine ligase catalytic subunit transcription indirectly via NF-kappaB and AP-1. Mol Cell Biol. 2005;25:5933-46 pubmed
    Glutamate-cysteine ligase catalytic subunit (GCLC) is regulated transcriptionally by Nrf1 and Nrf2. tert-Butylhydroquinone (TBH) induces human GCLC via Nrf2-mediated trans activation of the antioxidant-responsive element (ARE)...
  44. Li H, Shi N, Zhong Y, Dai Z. [Time course of gene expression of gamma-glutamylcysteine synthetase subunit and Nrf2 in brain tissues of rats exposed by deltamethrin]. Wei Sheng Yan Jiu. 2006;35:130-4 pubmed
    ..gene in rats cerebral cortex under the experimental condition. ..
  45. Tran P, Parker S, LeRoy E, Franklin C, Kavanagh T, Zhang T, et al. Adenoviral overexpression of the glutamylcysteine ligase catalytic subunit protects pancreatic islets against oxidative stress. J Biol Chem. 2004;279:53988-93 pubmed
    The catalytic subunit of glutamylcysteine ligase (GCLC) primarily regulates de novo synthesis of glutathione (GSH) in mammalian cells and is central to the antioxidant capacity of the cell...
  46. Tu Z, Anders M. Identification of an important cysteine residue in human glutamate-cysteine ligase catalytic subunit by site-directed mutagenesis. Biochem J. 1998;336 ( Pt 3):675-80 pubmed
    ..These results indicate that cysteine-553 in hGLCLC is involved in heterodimer formation between hGLCLC and hGLCLR. ..
  47. Kondo T, Yoshida K, Urata Y, Goto S, Gasa S, Taniguchi N. gamma-Glutamylcysteine synthetase and active transport of glutathione S-conjugate are responsive to heat shock in K562 erythroid cells. J Biol Chem. 1993;268:20366-72 pubmed
    ..It is also suggested that the regulatory site of the expression of these enzymes by heat shock is independent of that by EP. ..
  48. Misra I, Griffith O. Expression and purification of human gamma-glutamylcysteine synthetase. Protein Expr Purif. 1998;13:268-76 pubmed
    ..8, 0.1, 1.3, and 0.4 mM, respectively. Recombinant human gamma-GCS, like native rat gamma-GCS, is feedback inhibited by glutathione and is potently inhibited by buthionine sulfoximine and cystamine. ..
  49. Lebo R, Kredich N. Inactivation of human gamma-glutamylcysteine synthetase by cystamine. Demonstration and quantification of enzyme-ligand complexes. J Biol Chem. 1978;253:2615-23 pubmed
    ..The methods used permit the calculation of cystamine inactivation rates for most of these enzyme forms and also give values for the equilibrium constants describing their formation...